Role of Fe intercalation on the electronic correlation in resistively switchable antiferromagnet Fe$_{x}$NbS$_2$

Abstract

Among the family of intercalated transition-metal dichalcogenides (TMDs), Fe$_{x}$NbS$_2$ is found to possess unique current-induced resistive switching behaviors, tunable antiferromagnetic states, and a commensurate charge order, all of which are tied to a critical Fe doping of $x_c$ = 1/3. However, the electronic origin of such extreme stoichiometry sensitivities remains unclear. Combining angle-resolved photoemission spectroscopy (ARPES) with density functional theory (DFT) calculations, we identify and characterize a dramatic eV-scale electronic restructuring that occurs across the $x_c$. Moment-carrying Fe 3$d_{z^2}$ electrons manifest as narrow bands within 200 meV of the Fermi level, distinct from other transition metal intercalated TMD magnets. These states strongly hybridize with itinerant electrons in TMD layer, rapidly lose coherence above $x_c$, and drive a transformation of the magnetic ground state via modification of the effective Fe-Fe exchange interaction. These observations resemble the exceptional electronic and magnetic sensitivity of strongly correlated systems upon charge doping, shedding light on the tunability of magnetic exchange interactions beyond nearest-neighbor and electronic correlation in magnetic TMDs.

Figures (4)

• Figure 1: Structural and magnetic property of intercalated TMD magnets. (a) The crystallographic structure and Brillouin zone of 3$d$ metal intercalated TMDs M$_x$TA$_2$ with $x$ = 1/3. Brown and Green hexagonal traces circumscribe the in-plane Brillouin zones for M$_{1/3}$TA$_2$ and TA$_2$ respectively. (b) Depiction of the Heisenberg exchange terms between in-plane and out-of-plane nearest, next-nearest, and third-nearest neighbor intercalant ions in M$_{x}$TA$_2$. (c) Compilation of the Curie-Weiss temperatures for various M$_x$TA$_2$ systems with $x$ = 1/3 TMD1968TMD1970TMD1971TMD1975TMD1976parkin1980ghimire2018VNbS_1VNbS_2CrTaSCrNbSe_1CrNbSe_2MnTaSFeNbS_CWFeTaS_1FeTaS_2CoNbSCoTaSNiNbTaS.
• Figure 2: ARPES measurement of Fe$_{x}$NbS$_2$ across different Fe stoichiometry. (a) Energy-momentum cut along $\Gamma$-$M$-$K_0$ with different Fe stoichiometry. (b, c) Evolution of the position of S 3$p$ and Nb 4$d$ derived bands and number of holes calculated using Luttinger theorem with increasing Fe stoichiometry. Data for $x$ = 0 (hollow points) corresponds to $k_z$ = 0 and are extracted from Fig. 1 (c) (DFT calculated band structure) of NbS2ARPES. (d) Constant energy contours integrated between $E_B$ = 0.2 eV and 0.1 eV for $x$ = 0.30. Purple arrows indicate Fe-derived bands. Axis labels $k_{\Gamma M}$ and $k_{\Gamma K}$ mark directions to high-symmetry points in the Fe$_{1/3}$NbS$_2$ Brillouin zone. (e) Evolution of spectral weight of the Fe-derived bands with increasing Fe stoichiometry. Spectral weight integrated between [0,1] eV binding energy and $\pm 0.2$ Å$^{-1}$ of $\Gamma$.
• Figure 3: Mixed dimensionality and hybridization between Fe 3$d$ and Nb 4$d$ states. (a) Energy-momentum cut along $\Gamma$-$M$-$K_0$ and $A$-$L$-$H_0$ for $x$ = 0.30 collected at LV (upper panel) and LH (lower panel) polarizations, respectively. The black, red and blue dash lines are visual guides to compare band energy positions. (b-d) Scatter points tracking $k_z$ dispersion for Fe-derived bands (black and red circles) and Nb-derived bands (blue circles) extracted from EDC fitting results (Fig. \ref{['SI-SI_kzmap']}). (e) Data reproduced from Fig. \ref{['FNSarxivv2:fig2']} (a) on $x$ = 0.32, highlighting orbital contributions using a matching color scale to Fig. \ref{['FNSarxivv2:fig2']} (d). (f) Fitted trajectory extracted from (e).
• Figure 4: (a) Projected electronic density of states (DOS) of the Fe spin sublattices in Fe$_{1/3}$NbS$_2$ for AFM stripe (left) and AFM zigzag (right) magnetic phases as computed by DFT. The Fe 3$d$ orbitals are further projected by their $t_{2g}$ and $e_{g}$ irreducible representation characters as well as their spin channels of spin-up (bonding) and spin-down (anti-bonding) respectively (indicated by different colors). (b) Orbital diagrams depicting the Fe 3$d$ band splitting and occupation below and above the critical doping boundary $x_c = 1/3$.